Update on vaccine-derived polioviruses–worldwide, January 2008-June 2009

In 1988, the World Health Assembly resolved to eradicate poliomyelitis worldwide. Subsequently, the Global Polio Eradication Initiative of the World Health Organization (WHO) reduced the global incidence of polio associated with wild polioviruses (WPVs) from an estimated 350,000 cases in 125 countries in 1988 to 1,651 reported cases in 2008 and reduced the number of countries that have never interrupted WPV transmission to four (Afghanistan, India, Nigeria, and Pakistan). Under current WHO plans, when the goal of eradicating all WPV transmission is attained, oral poliovirus vaccine (OPV) use worldwide eventually will be discontinued. However, because vaccine-derived polioviruses (VDPVs) can produce polio outbreaks in areas with low rates of Sabin OPV coverage and can replicate for years in immunodeficient persons, enhanced strategies are needed to limit emergence of VDPVs. This report updates previous summaries and describes VDPVs detected worldwide during January 2008-June 2009. During this period, 1) two new outbreaks of circulating VDPVs (cVDPVs) (accounting for 4-20 cases) were identified in the Democratic Republic of Congo and Ethiopia; 2) a previously identified outbreak in Nigeria ultimately resulted in a cumulative total of 292 cases; 3) two newly identified paralyzed immunodeficient persons in Argentina and the United States were found to excrete VDPVs; and 4) isolated VDPVs were found among persons and environmental samples in 11 countries. All countries need to maintain 1) high rates of poliovirus vaccination coverage to prevent VDPV spread and 2) sensitive poliovirus surveillance to detect VDPVs.